The Adamantium "Rift"

Since the Dawn of Time, there has been a massive gap in one of the most-used materials chains in the game: the iron/iron alloy chain.

00 Int: Tin -> Copper
00 Int: Copper -> Bronze
05 Int: Bronze -> Iron
10 Int: Iron -> Steel
15 Int: Steel -> Meteoric Steel
???
40 Int: Meteoric Steel -> Adamant

This has always felt a little silly. Any ideas on how to smooth this curve out a bit, while preserving balance?

There was a bunch of ideas in this thread: https://attnam.com/topics/Titanium-and-other-metals

I guess we just bridge it with some more materials?